Conventionally, as the methods of removing thrombi, there is a method of inserting a catheter into a thrombus portion and dissolve the thrombus by injecting thereinto a thrombolytic agent such as streptokinase (e.g., Japanese Patent Unexamined Publication No. 57-173065); a method of withdrawing a catheter while maintaining the balloon of a balloon catheter in an expanded state and, at the same time, removing a thrombus (e.g., Japanese Patent Examined Publication No. 49-16472); and a method of clamping a thrombus portion by two expanded balloons, softening the thrombus by injecting a thrombolytic agent thereinto, and withdrawing a catheter and at the same time removing the thrombus (e.g., Published Japanese Translation of PCT Appln., Publication No. 58-501983).
However, even if the thrombolytic agent is injected locally through the catheter, there is a drawback in that the thrombolytic agent flows into normal terminal blood vessels and the like, thereby entailing the risk of hemorrhage in the terminal blood vessels and the like. Further, in the case where the catheter was withdrawn while maintaining the balloon of the balloon catheter in a expanded state to simultaneously remove the thrombus from the body, there was the risk of causing damage to the inner wall of a blood vessel since a safety measure against a tensile stress applied to the inner wall of the blood vessel has not been taken. In the case where a catheter provided with two balloons, was used as a similar method of removing a thrombus, when the catheter was to be used to clamp a thrombus 27 between two balloons 31, 32 (see FIG. 7), the balloon 32 located closer to the tip of a catheter 30 needed to be inserted from a position 34 in front of a thrombus 27 up to a position 35 which is deeper than that of the thrombus 27, so that there was the danger of pushing, by the balloon 32, the thrombus 27 in the inserting direction 33 as illustrated in FIG. 7, thereby moving the thrombus 27 to another part, such as a terminal blood vessel.
Furthermore, as a method of mechanically removing a thrombus, a drill bit is provided at the tip of a bar-like member, the drill bit being made to rotate by rotating the bar-like member, and the thrombus is crushed by the drill bit rotation. With this method, however, a torsional stress is applied to the inner wall of the blood vessel, so that there is a drawback in that the blood vessel may be cut off by the stress, and adjustment of the number of revolutions and the like is hence made difficult.
Further, a surgical apparatus using ultrasound has recently become known in which an ultrasonic probe connected to a source of ultrasonic vibration is used to crush tissue, a calcification aggregate, thrombus, or the like by mechanical vibrations of an ultrasonic frequency at the tip of the ultrasonic probe, and the crushed tissue, calcification aggregate, thrombus, or the like is removed through an inner hole provided in the ultrasonic probe (e.g., Japanese Patent Unexamined Publication Nos. 60-5139 and 49-21989). With such a device, however, since the ultrasonic probe having a working portion which mechanically vibrates at an ultrasonic frequency was not flexible, there was a drawback in that it would be difficult to insert it into a curved blood vessel or a tubular tissue inside the body.